1. Technical Field
The inventive concept relates to a semiconductor device, and more particularly, to a semiconductor device and a method of fabricating the same.
2. Related Art
With demands on low power consumption from memory devices, next-generation memory devices with non-volatility and non-refresh have been researched. Phase-change random access memory (PCRAMs), which are examples of such next-generation memory devices, store data using a resistance difference between an amorphous state and crystalline state of a phase-change layer (e.g., a chalcogenide compound) created by an electric pulse to the phase-change layer.
In conventional PCRAMs, a MOS transistor or a PN diode is employed as a switching element. When the MOS transistor is used as the switching element, improvement in integration of the PCRAM is limited. When the PN diode is used as the switching element, a plurality of PN diodes are electrically connected to each other through an N+ region formed in a surface of an active region. Thus, driving currents of cells are different from each other due to large resistance of the N+ region. Therefore, a PCRAM having an improved design and a method a manufacturing such an improved PCRAM is necessary.
In recent years, a Schottky diode has generally been used as the switching element of the conventional PCRAM.
The conventional PCRAM employs a metal word line on a semiconductor substrate and a Schottky diode formed on the word line.
The Schottky diode includes a barrier metal layer in contact with the word line and a P+ polysilicon layer formed on the barrier metal layer.
In the conventional PCRAM employing the Schottky diode, a height of the barrier metal layer has to be increased to control an off current and a work function of the barrier metal layer has to be lowered in order to increase the height of the barrier metal layer.
When the conventional PCRAM is fabricated, metal used for the word line or the barrier metal layer may include aluminum (Al), tungsten (W), titanium nitride (TiN), or copper (Cu). However, since a subsequent thermal process is performed at a temperature of 700° C. or more, it is difficult to use a metal material such as Al or Cu. Thus TiN is typically used as the metal for the word line or the barrier metal layer.
However, TiN has large work function, for example, approximately 4.7 eV to degrade performance of the PCRAM.